My father had a saying "An automatic choke is smarter than all drivers, and most mechanics!" He was a man of great wisdom, and I miss him every day. Converting back to an auto choke is a pretty simple project unless someone has done some modifying to the lever arm that moves the choke flap back and forth. Carb King should be able to provide the proper choke cover for your carb, and whatever attaching hardware might be missing. Then it's simply a matter of unplugging the port you blocked off and installing a "choke stove"- - - -a sheet metal item that clamps onto one of the exhaust manifold runners and a piece of steel tubing (brake line works) to connect the choke stove to the carburetor port. Universal-fit choke stoves are available on Ebay for very reasonable prices. Then the carb draws a small volume of air through the tube and provides clean hot air (not exhaust gas) to the choke assembly to make the bimetal spring in the choke to relax and allow the choke flap to open as the engine warms up. That "vacuum leak" you're experiencing is actually a small controlled airflow through the carburetor that shouldn't affect the ability to make idle mixture adjustments or make the engine run rough.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!